<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }
        div {
            position: absolute;
            width: 20vw;
            height: 20vh;
        }
        #a {
            background: #dd0b0b;
            top: 15%;
        }
        #b {
            background: #5fff58;
            top: 25%;
        }
        #c {
            background: #ffb063;
            top: 0;
        }
        video {
            position: absolute;
        }
    </style>
</head>
<body>
<div id="a">红</div>
<div id="b">绿</div>
<video width="600px" height="400px" src="1.mp4" type="audio/mp4"></video>

<div id="c">橙</div>
<script>
    document.body.onclick = function () {
        var a = document.getElementsByTagName("video")[0];
        a.setAttribute("style","z-index: 1000; height: 800px;")
    }
</script>
</body>
</html>